To provide a controlling circuit for a motor without complicated circuit configuration, with superior responsiveness to a phase-difference signal, and with less signal variation due to heat.

The rotation controlling circuit of the motor has a PWM controlling circuit, a rotating-speed sensor, a reference-signal generating circuit 10, a phase comparator, and a divider to divide a rotating-speed signal for detection. A phase difference between the signal from the divider and the signal based on the reference signal is determined by the phase comparator, and the phase-difference signal is supplied to the PWM controlling circuit.